Orthopedic casts for use in the treatment of bone fractures or other conditions requiring immobilization of the body member are generally formed from a sheet of fabric or scrim material impregnated with a substance which hardens into a rigid structure after the sheet has been wrapped around the body member.
The orthopedic casts now most commonly used are comprised of a fiberglass scrim impregnated with a water-curable isocyanate-functional prepolymer. These casts when cured have a higher strength to weight ratio than plaster-of-paris, are impervious to water and provide excellent radiolucency. U.S. Pat. No. 4,411,262 (von Bonin) and U.S. Pat. No. 4,502,479 (Garwood) disclose water-curable isocyanate-functional prepolymers useful in orthopedic bandages.
The prepolymer typically includes a tertiary amine catalyst in an amount selected to optimize curing time. After the resin-impregnated scrim has been immersed in water, sufficient "working time", e.g., 3 to 5 minutes, should be provided in which the wrapping is accomplished and the cast is manually molded into shape. However, after the cast is shaped, the resin should harden rapidly, typically in 15-30 minutes and preferably less, into a rigid, high-strength, weight-bearing cast.
U.S. Pat. No. 4,376,438 (Straube et al.) discloses an orthopedic casting material wherein the tertiary amine catalyst is chemically linked to the polymer portion of the isocyanate functional prepolymer. No separate catalyst is required.
U.S. Pat. No. 4,502,479 (Garwood et al.) discloses the use of tertiary alkanolamines, e.g., dimethylethanolamine and dimethylaminodiethyl ether, as catalysts in the curing of a water-curable isocyanate functional prepolymer. At concentrations which do not adversely affect shelf stability, these simple catalysts do not cure as fast as desired by many experienced cast appliers.
U.S. Pat. No. 4,433,580 (Yoon) discloses the use of 2,2'-dimorpholinyldiethyl ether (DMDEE) as a catalyst in the cure of a water-curable isocyanate-functional prepolymer on an open-weave fibrous substrate to form an orthopedic bandage. The use of DMDEE is said to provide an orthopedic bandage having increased shelf-stability and acceptable set time.
Commercially available orthopedic bandages containing DMDEE typically contain about 2-3 percent by weight DMDEE (about 7.5-10 mole percent). These commercially available orthopedic bandages, while having acceptable shelf stability and set time, do not exhibit superior early strengths. Superior early strengths are particularly advantageous in the case of leg casts which must be weight bearing in a relatively short time after application to permit the patient to ambulate.
A journal article, H. Igarishi, et al., "On the Synthesis and Pharmacology of Basic-sec,tert-Alcohol and Derivatives", Yakugaku Zasshi, 93, 554, 563-564 (1973) discloses the preparation of a mixture of 1-methyl-2-N-morpholinoethyl 2'-morpholinoethyl ether dihydrochloride and 2-methyl-2-N-morpholinoethyl 2'-morpholinoethyl ether dihydrochloride and a mixture of di(1-methyl-2-N-morpholinoethyl) ether dihydrochloride and 2-methyl-2-N-morpholinoethyl 2'-methyl-2'-N-morpholinoethyl ether dihydrochloride and the pharmacological, e.g., antispasmodic and analgesic, activities of the respective mixtures.